Obviously, there's more differentiating these baddies than gender. There are certain traits that define how the siblings of darkness are written into a story.

Let's start with Mary Sue, the more prevalent of the two. Mary Sue authors are often preteen girls, though they range anywhere from approximately eleven up through the mid-twenties. Rarely will you see a Suethor above the age of twenty, at least not in my personal experience; it occurs, but these Sues have better planning. That does not make them a lesser evil. It only makes them a more readable, legible evil, which could be considered far worse than the illiteracy that dominates preteen Sues.

As younger girls (and women), Suethors display certain obligatory desires, usually played out in their stories with as much detail as they can muster. And, as you may already know very well, this detail can thoroughly trample the boundaries of excessive. Character descriptions can become ludicrous, with so many details - very precise details, leaving nothing to the imagination - that many anti-Sue activists refer to them as "police reports." Hair and eye color are, of course, a mainstay, but the Suethor typically adds information about complexion, height, and always will say something about the Mary Sue's body type. She may also add in clothing descriptions worse than those in fashion magazines, with full on measurements occasionally included.

On to the aforementioned desires. Romance is a Sue story staple, showing up in big and (sometimes) small ways throughout the story. The entire plot of a story can focus on one or more romances that the Mary Sue has with canon - or even other original - characters. It can become so important, in fact, that the canon plot is swept to the side in favor of a kissing scene or, worse, a sex scene. Mary Sue sex is, at best, the kind of cliché "tender and moving" sex that one encounters in poor romance novels. Description is still key in such types of sex scenes, with flowery, purple prose running rampant. Sue's body parts are often detailed here, as are her partner's, though the terms used for genitalia are generally ambiguous.

Next comes the Gary Stu, the less common but still terrible second half of the twosome. His authors tend to be teenage boys and young men. The age range here is perhaps thirteen to the mid- or late twenties. However, the more common brand are teenage Stuthors, who, with their raging hormones and desire for masculinity, need a venting device. Sometimes, a female author may even write a Gary Stu. As a rule, Stuthors of the first kind - the teenage ones - are like preteen Suethors in their lack of care for rules of basic language. The second kind of Stuthor may pay attention, but, like their older Suethor counterparts, can range from very sloppy to passably good. The third kind makes the story even less believable by implanting more...feminine touches into these pillars of manliness. All in all, this makes all Stus as bad as their sisters.

Detail in Stu stories is nothing like that of the Sue stories. Except for Stuthors of the third kind, the authors do not succumb to purple prose. They make things stark and plain, only embellishing when it means that the Stu will look even better. He is described, of course, and often at length, but there is none of the adjective rape that occurs in a Sue story. If there is, the Stuthor is either very interested in his image of his Stu, or "he" is really one of those third category Stuthors. The description is not quite police report material, but will include body type information - from muscle structure to height - and hair and eye colors. Any other physical description is often limited to clothes, including armor, and accessories (as in weaponry). The detail is also vastly different in Gary Stu sex scenes, which are idealized by males and therefore include less of a "lovemaking" feel and more of a "fucking" feel. The woman can be objectified, and the Stu is shown as a perfect breeding machine. Terminology, unfortunately, is embarrassing and even clunky, especially when discussing the Stu's genitalia and what he is doing to his bedmate. All of the above, though, veers more towards Mary Sue detail when a third category Stuthor is involved.

The author's desires in a Stu story are for strength and ofttimes for sexual action. Strength is displayed frequently, outdoing canon males (and of course females) for the spotlight. The plot focuses on Gary Stu's powers, usually saving the day, and may wander off course for a sex scene now and then. For the most part, Gary Stu is the conquering hero. He wins the day and the beautiful damsel's heart, all the while either annoying the lesser canon males, or inspiring them with utter amazement.

In the end, both are wrong, both are almost always poorly written - and even when they are not poorly written in the literary sense, the characterizations and events are - and both are to be avoided at all costs. With differences in mind, the exceptions to the rule (such as Suethors writing with sparse detail, or Stuthors adding in overdone adjectives and adverbs) become more obvious, and all become more odious.

If being more odious is possible.